Re: [PATCH v3 08/14] powerpc/xmon: Remove store_inst() for patch_instruction()

[Nicholas Piggin <npiggin@gmail.com>]

Jordan Niethe's on February 26, 2020 2:07 pm:
> For modifying instructions in xmon, patch_instruction() can serve the
> same role that store_inst() is performing with the advantage of not
> being specific to xmon. In some places patch_instruction() is already
> being using followed by store_inst(). In these cases just remove the
> store_inst(). Otherwise replace store_inst() with patch_instruction().
> 
> Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> ---
>  arch/powerpc/xmon/xmon.c | 13 ++-----------
>  1 file changed, 2 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index 897e512c6379..a673cf55641c 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -325,11 +325,6 @@ static inline void sync(void)
>  	asm volatile("sync; isync");
>  }
>  
> -static inline void store_inst(void *p)
> -{
> -	asm volatile ("dcbst 0,%0; sync; icbi 0,%0; isync" : : "r" (p));
> -}
> -
>  static inline void cflush(void *p)
>  {
>  	asm volatile ("dcbf 0,%0; icbi 0,%0" : : "r" (p));
> @@ -882,8 +877,7 @@ static struct bpt *new_breakpoint(unsigned long a)
>  	for (bp = bpts; bp < &bpts[NBPTS]; ++bp) {
>  		if (!bp->enabled && atomic_read(&bp->ref_count) == 0) {
>  			bp->address = a;
> -			bp->instr[1] = bpinstr;
> -			store_inst(&bp->instr[1]);
> +			patch_instruction(&bp->instr[1], bpinstr);
>  			return bp;
>  		}
>  	}
> @@ -913,7 +907,7 @@ static void insert_bpts(void)
>  			bp->enabled = 0;
>  			continue;
>  		}
> -		store_inst(&bp->instr[0]);
> +		patch_instruction(&bp->instr[0], bp->instr[0]);

Hmm that's a bit weird. Can you read instructions into a local variable
first, do the checks on them, then patch them into their execution
location?

Otherwise, good cleanup.

Thanks,
Nick